This relates to a system that facilitates positioning a tool in a work space or at a work site, such as for example a construction site. When the interior of a building is being finished, connectors, anchors and the like are attached to the floors, ceilings and other structures in the building and cuts are made and holes drilled using power saws and drills. All of this must be accomplished using special power tools at predetermined locations, requiring that the tools be operated at numerous precisely defined positions in the building. For example, nail guns, power saws, powder anchor tools, and the like are used to nail, cut, install fasteners, and perform other operations at predetermined points within the building with little error. In any building, a large number of electrical, plumbing, and HVAC components must be properly sited and installed, usually with power tools. Additionally, finishing a building interior also requires that a number of different tools that are not powered be operated at precisely defined positions, such as for example reinforcement bar scanners. Positioning both power tools and non-power tools must be accomplished quickly and with some precision with respect to the surrounding walls, ceilings and floors as they are roughed in. Typically, it has required a significant amount of labor to lay out various construction points at such a construction site. Teams of workers have been needed to measure and mark predetermined locations. It will be appreciated that this process has been subject to errors, resulting from measurement mistakes and from accumulated errors. Further, the cost of this layout process and the time needed to perform the layout process have both been significant.
Ranging radios offer an excellent alternative to GPS receivers for positioning applications where GPS reception is not available, such as inside a building, or where use of GPS receivers is not reliable. For example, GPS receivers require line-of-sight access to multiple satellites in order to function properly. Use of GPS receivers may not be possible in some operational settings, such as when work is being performed indoors, underground, or in cluttered environments.
Ranging radios, operating at ultra wideband (UWB) frequencies, provide very accurate measurement of distances between the radios, using time-of-flight analysis. When ranging is accomplished from multiple fixed position radios to a target radio, the relative, three-dimensional position of the target radio is accomplished through trilateration. To perform a range measurement, an originating ranging radio transmits a packet consisting of a synchronization preamble and a header. The header contains the range command with the address of the destination radio that is requested to respond to the packet. The originating radio resets its main counter at the time of this transmission, establishing a local time-zero reference. When the destination ranging radio receives the range request addressed to it, it records the time of receipt, and replies with its own packet, including the time of receipt and the time of the responding transmission in the header. The originating radio receives the ranging packet back from the destination radio, records its time of receipt and latches its main counter. The range value is then calculated and recorded, utilizing the time information to compensate for the differences in the timing clocks at the two radios.
Other location determination systems have been used in the past for building layout including, for example, robotic total stations. The total station is positioned at a fixed, known location and directs a beam of laser light at a retroreflective target. As the target moves, robotics in the total station redirect the beam of light so that it tracks the target. By measuring the time of travel of the beam from the total station to the retroreflective target and then back to the total station, the distance to the target is determined. The directional orientation of the beam to the target is also measured. Since the dimensional coordinates of the total station are known, the dimensional coordinates of the retroreflective target can easily be determined.
Although position determination systems, such as ranging radio systems and robotic total station systems, can facilitate and speed the layout process, nevertheless the layout process has continued to be lengthy, tedious, and expensive.